Acyclovir has become an antiviral agent of choice for the treatment of genital herpes simplex infections. Two related compounds, 6-deoxyacyclovir and the 6-deoxy-6-amino analog are being developed as agents for treating herpes infections. However, these agents are not without side effects. For example, skin rashes and renal impairment have been reported as side effects for acyclovir (see Physicians' Desk Reference, 41st ed., Medical Economics Inc., Oradell, N.J., USA, 1987, pp 814-818). Hence, safety as well as cost advantages should be realized if these agents could be formulated in a manner so that their activity is enhanced.
Unexpectedly, we have found that the antiviral activity of acyclovir, or a functionally equivalent derivative thereof, can be significantly enhanced by combining the same with the antibiotic bacitracin. This finding is even more surprising when viewed in the light of some of the published reports on bacitracin. Namely, A. Alarcon et al., Antiviral Research, 4, 231 (1984) have reported that bacitracin, when used alone, is inactive against herpes simplex virus type 1 (HSV-1); notwithstanding an earlier disclosure by J. Z. Krezanoski in U.S. Pat. No. 4,188,373, issued Feb. 12, 1980, incidentally listing bacitracin in a long .list of antimicrobials for treating fungal and viral diseases without distinguishing which antimicrobial is used for which purpose. Also, R. Segal et al., U.K. patent application 2167296, published May 29, 1986 have proposed a rather complex mixture of bacitracin, neomycin and glycyrrhizin for treating oral infections. Thus, the enhancement of the antiviral activity found with the straight forward combination of this invention represents an unexpected turn of events. As a result, however, a relatively safe and economical pharmaceutical formulation and method for treating herpes infections are realized.